The above criterion on the pulse duration should typically be fulfilled at the Gamma Factory [1]}, [2]}, which can be expected to provide gamma pulses of duration \(T\gtrsim 160\,{\rm fs}\) . At the same time, the collision point of the gamma beam with the high-intensity laser beam should be sufficiently separated from the source of the gamma photons such that generically \(w_\gamma \gg w_0\) .
